Anecdotally, in my case, mindfulness as a result of meditation and similar mind-calming practices (like jogging, stretching) helped me to advance my career from a dev to a team lead and eventually helped me to get a courage to pursue my dreams of being an entrepreneur.
I can conclude that in my case, it did not decrease my motivation but helped me to:
1. overcome my anxiety and become a better employee
2. see what I truly want and get rid of the mental stuff the others (meaning the corporation) imposed on me (following the said corporation's goals)